The present invention relates to an operating arm on an earthmoving vehicle, and in particular to a control for an operating arm that is move up and down by a hydraulic system.
In an earthmoving vehicle such as an excavator, the operating arm links, such as the boom arm, are usually moved by a number of double-acting linear actuators.
Fluid flow to the actuators is controlled by a central hydraulic supply and control unit. Each actuator is associated with a proportional distributor valve, which is connected by hydraulic lines to the actuator chambers. The control unit regulates the hydraulic fluid pressure and the fluid flow to and from the actuator chambers during the operation of the arm, as for example in the digging mode.
However, the operating arm of these vehicles can also be used for moving loads over distances. Consequently, a regulating valve is provided in series between each actuator and the associated distributor valve to guard against loss of hydraulic fluid in the event of damage to the hydraulic lines or other fluid components. The regulating valve prevents the load from dropping when the operating arm descends rapidly.
The addition of a regulating valve, however, affects the response times when the arm is used in normal operations, such as in the digging mode. Traditionally the response times are calculated and set solely with reference to the distributor valve. However the distributor valve and regulating valve operate in contrast with each other during transient operating conditions.